Rigid urethane-modified polyisocyanurate (PIR) foams are in general prepared by reacting a stoichiometric excess of polyisocyanate with isocyanate-reactive compounds (usually a polyol) in the presence of a blowing agent, surfactants and catalysts. One use of such foams is as a thermal insulation medium as, for example, in buildings. Urethane-modified polyisocyanurate foams exhibit better fire retardancy, reduced smoke emission in fire situations, and greater thermal stability than polyurethane foams, in general, due to the presence of the isocyanurate groups. Higher index PIR foams are increasingly desirable in construction applications due to more stringent fire regulations and the need for low smoke systems. However, it has shown very difficult to achieve good isocyanurate conversion with slow reacting foam systems as is the case in thick (20 cm) lamination panels and in discontinuous panels. Another disadvantage of PIR foams, in general, is their poor adhesion to facer materials in building panels.